As computers and data processing equipment have grown in capability, users have developed applications that place increasing demands on the equipment. Thus, there is a continually increasing need to process more information in a given amount of time. Computers and data processing equipment include electronic circuits coupled to each other by electrical conductors. The various electrical circuits perform various tasks in the processing of information, and the electrical conductors allow signals representing information to be passed between the electrical circuits to allow processing of the information to be completed.
Traditionally, digital signals having two voltage levels, one voltage level to represent a binary zero and another voltage level to represent a binary one, have been used to communicate information between electronic circuits. To avoid interference, the electrical conductors have traditionally been constrained to pass a single voltage level, representing one bit of information, in one direction at any given point in time. Given this constraint, attempts to increase the amount of information processed per unit time have generally involved either increasing the number of electrical conductors so that several bits of information can be processed in parallel and increasing the rate at which the signals are transmitted over the electrical conductor.
The results of the efforts to process more bits of information in parallel can be seen in the increasing bus widths of modern computers and data processing equipment. The result of efforts to increase the rate at which signals are transmitted over an electrical conductor can be seen in the increasing clock frequency of modern computers and data processing equipment. Efforts to continue increasing the amount of information that can be processed in a given amount of time are hindered buy the difficulties of fabricating large numbers of parallel electrical conductors of microscopic dimensions that reliably pass signals at high frequencies, for example, frequencies extending into the microwave region of the spectrum. Thus, a technique is needed to increase the rate at which information can be processed without relying merely on increasing bus width or increasing frequency.